1. Field of the Invention
The present invention relates generally to ignition coils for developing a spark firing voltage that is applied to one or more remotely mounted spark plugs of an internal combustion engine.
2. Description of the Related Art
An ignition coil configured to be mounted in an automotive engine compartment remotely from a spark plug is known that includes a so-called xe2x80x9csegmentxe2x80x9d wound secondary winding, as seen by reference to U.S. Pat. No. 5,015,982 issued to Skinner et al. Skinner et al. disclose an ignition coil configured for operation in a waste spark system having a magnetically-permeable core, a primary winding, and a secondary winding disposed on a secondary winding spool. The first and second ends of the secondary winding are connected to respective high-voltage towers for connection to remotely installed spark plugs. The secondary winding spool disclosed in Skinner et al. further includes a plurality of axially spaced and circumferentially extending ribs, which, in combination with the outside diameter (O.D.) of the spool body, define a plurality of axially spaced winding slots. Skinner et al. disclose that each of the winding slots contain a coil winding.
Remote or separately mounted ignition coils conventionally employ a segmented secondary winding such as disclosed in Skinner et al. However, there are drawbacks to the segmented secondary winding configuration. First, a so-called crossover region of the secondary winding spool (i.e., a region to allow the secondary winding to transition between winding slots) is relatively difficult to fill with conventionally employed dielectric materials, such as epoxy potting material. This difficulty is worsened when polyester material is used. The foregoing described failure to fill certain areas with epoxy potting material leads to certain failure modes due to the lack of the needed electrical insulation in the secondary circuit.
Another drawback with segmented wound secondary windings involves the crossover region itself, where certain stresses on the winding increase the likelihood of failure. A third drawback is that the axially spaced ribs increase the size the ignition coil itself. In particular, since the ribs of the spool extend radially outwardly relative to the centrally disposed core, the radial size of the coil is also increased. Notably, a magnetically-permeable shield, which is conventionally included to provide, among other things, a flux return path, is conventionally also radially moved outwards a corresponding distance. This increased outward spacing of the shield leads to a requirement of including so-called xe2x80x9cpole piecesxe2x80x9d at opposing axial ends of the core in the ignition coil so as to bridge the now increased core-to-shield radial distance (i.e., to complete the magnetic circuit). For example, Skinner et al. referred to above disclose such pole pieces. The pole pieces, however, increase the cost, size and weight of the ignition coil.
It is also known, however, to provide a so-called xe2x80x9cpencilxe2x80x9d ignition coil (i.e., a relatively slender ignition coil configured to be mounted directly above and to a spark plug) having a secondary winding wound on a spool in accordance with a so-called xe2x80x9cprogressivexe2x80x9d winding approach, as seen by reference to U.S. Pat. No. 5,929,736 issued to Sakamaki et al. Sakamaki et al. disclose an ignition coil configured to be mounted directly to a spark plug but which has a secondary winding that is wound in accordance with a progressive winding technique. The secondary winding spool disclosed in Sakamaki et al. therefore does not have the axially spaced ribs defining winding slots described above. However, it is not always possible or desirable to mount an ignition coil directly to the spark plug. Therefore, in many instances, the coil must be mounted remotely, and therefore the teachings of Sakamaki et al. cannot be followed.
There is therefore a need to provide an improved ignition coil that minimizes or eliminates one or more of the shortcomings as set forth above.
An ignition coil assembly in accordance with the present invention is characterized by the features specified in claim 1.
An ignition coil assembly in accordance with the present invention includes a progressive wound secondary winding that results in a smaller package than a comparable segment wound ignition coil assembly. The invention further eliminates failure modes associated with ignition coils of the type having a segment wound secondary winding. Moreover, due to significant reductions in size, certain components conventionally found on remotely-mounted ignition coils, such as so-called xe2x80x9cpole piecesxe2x80x9d can be eliminated, thus providing an ignition coil assembly that has fewer components, uses fewer materials, provides a simplified core structure, all at a lower cost, smaller size, and having a reduced weight compared to conventional designs.
These and other advantages are realized by an ignition coil assembly in accordance with the present invention, which includes a core formed of magnetically-permeable material extending along a main axis, a primary winding disposed about the core, a secondary winding disposed on a secondary winding spool also disposed about the core wherein at least one of first and second ends of the secondary winding is electrically connected to a high-voltage connector terminal configured for connection to a remotely disposed spark plug, a case formed of electrical insulating material, and a magnetically-permeable shield disposed outwardly of the case, characterized in that: the secondary winding is progressively wound on the secondary winding spool.